Magnetic domain wall memory is one type of memory. In a magnetic domain wall memory, a magnetic material is used as a portion to record information. Information is expressed by a magnetic domain structure formed by the magnetization of the magnetic material, the locations of the magnetic domains, or the spatial distribution of magnetization in the domain walls. Magnetic memory so-called “racetrack memory” is also one type of magnetic domain wall memory.
Arranging magnetic domains in a line in the magnetic material gives rise to high density information storage of a magnetic domain wall memory. Therefore, the magnetic material that stores information has a linear shape or a curved shape. When a current is applied in the direction in which the magnetic domains are arranged, the domain walls shift toward the direction in which the current flows. In the magnetic domain wall memory, this phenomenon is utilized to shift the domain walls, after the magnetization of an extended portion of the magnetic material is reversed, or after the magnetization state of part of the magnetic material is converted into an electrical signal. An information write/read operation is performed in this manner.
A large number of magnetic materials to record information are installed as nanowires at a high density in a direction being perpendicular to the wafer surface. With this arrangement, a large-capacity magnetic domain wall memory can be realized. Micromachining is performed on the wafer, to form a three-dimensional structure such as a hole-like or pillar-like structure, which becomes a template for the magnetic nanowire. A magnetic thin film is then formed on the surface of the three-dimensional structure, and is divided into minute parts, to form the nanowires. Alternatively, holes that are formed through an electrochemical reaction are filled with a magnetic material, to form the nanowires. In either case, the micromachining for fabrication of the nanowires or the electrodes, to be used for the electrochemical reaction, is necessary and then it results in higher manufacturing costs.